Scooterotica

mikeveslam wrote: So far for the gt 186 I have the following,

1. The gt 186 kit with head and 30mm reed manifold.
2. Gt chain guide
3. Li 150 gear box.
4. Electronic ignition with 2kg flywheel

So what crank and exhaust would you recommend and what results do they have on engine characteristics ?

This is how my GT was set up. With a 17t primary and an RS44 clubman. It would have benefitted from 4.8 gearing, to be fair. And would have been faster with it. But it was a nice touring set up. And lasted for quite a while as a work bike.
Good on fuel too, even with a 30 mil carb.
Easily the smoothest engine I've had.

Muttley McLadd wrote:

mikeveslam wrote: So far for the gt 186 I have the following,

1. The gt 186 kit with head and 30mm reed manifold.
2. Gt chain guide
3. Li 150 gear box.
4. Electronic ignition with 2kg flywheel

So what crank and exhaust would you recommend and what results do they have on engine characteristics ?

This is how my GT was set up. With a 17t primary and an RS44 clubman. It would have benefitted from 4.8 gearing, to be fair. And would have been faster with it. But it was a nice touring set up. And lasted for quite a while as a work bike.
Good on fuel too, even with a 30 mil carb.
Easily the smoothest engine I've had.

Cheers for the reply.

Rich,If I wanted to use a 115mm conrod and a 60mm stroke crank witha a DT 175 piston, does the piston need any modification? I see in the table you published that with this combination I barely wouldn´t change the port timming nor loose primary compression with the gain of a smoother engine thanks to the larger conrod.

Pepot wrote:Rich,If I wanted to use a 115mm conrod and a 60mm stroke crank witha a DT 175 piston, does the piston need any modification? I see in the table you published that with this combination I barely wouldn´t change the port timming nor loose primary compression with the gain of a smoother engine thanks to the larger conrod.

In a 186 the largest possible bore is 66.5 or tops 66.75. The DT175 starts at 66mm so this is a better piston/rod/stroke combination for Big Blocks. Other pistons in this range are the Blaster and IT175 (both 66-68mm and none need modifying).

The real question is define "Smooth"? If you are referring to vibration then this has little to do with rod, stroke and pistons.

With "smooth" I meant a smaller conrod angle and less friction of the piston against the cylinder walls. If fitting a DT piston means reboring almost to the maximum I'll abandone the idea of fitting it and try to compensate the loss of primary compression with a full circle crank using a 60 115 combination with an standard piston. Thanks for answering!